1. Field of the Invention
This invention relates to adhesives and resins, and processes for their preparation. More particularly, this invention relates to resin and adhesive compositions which can be particularly used in the manufacture of cellulose-based products, and more particularly paper products. Resins and adhesives of the present invention are produced by combining a water-soluble polymeric material which comprises a nucleophile, a phenolic material, and a component that serves to activate the phenolic material to make it reactive with the nucleophile of the polymer. Adhesives and resins produced according to the present invention are particularly useful in the paper making industry but their application is not limited thereto.
2. Background of the Invention and Related Information
Many compositions for resins and adhesives are known in the art. Most of these compositions, however, include components which can be considered environmentally "unfriendly," or even toxic. In addition, some existing adhesives and resins are, in themselves, environmentally "unfriendly" or toxic. There is, therefore, a need for resins and adhesives which are non-toxic and which are produced from non-toxic components.
The paper-making industry has long been concerned with ways of increasing the strength of wetted paper. Paper constructed without additional means of reinforcement will often fall apart upon rewetting. Paper which maintains its strength upon wetting is desirable in many applications, including bathroom tissue, paper towels, napkins, and the like. In addition, additives which increase the strength of wet paper often increase the dry strength of the same paper.
Many of the additives known in the art which can be used to increase the wet strength of paper take advantage of the chemical structure of the cellulose found therein. The cellulose found in paper products often has carboxylate and hydroxyl moieties exposed along its chain. Through the use of reactive additives, crosslinks can be formed between these moieties in the chains of cellulose in the paper, thereby increasing the strength of the paper. Alternatively, some additives do not react with the cellulose, but increase the paper strength by some other, unknown mechanism. In either case, the additives are usually chosen for their ability to adhere to the pulp, and for their ability to form a structural network which can repress cellulose fiber swelling, thereby inhibiting separation of the fiber-fiber contacts upon wetting.
Some of the earliest wet-strength resins were condensation products of urea and formaldehyde, with polyamine added to make the resin cationic. Such resins appear only to impart wet-strength via self-crosslinking. However, resins formed from melamine and formaldehyde appear to crosslink the cellulose directly. Polyamide and epichlorohydrin form resins which react with the cellulose carboxylate groups. At higher concentrations, polyamide/epichlorohydrin resins appear to form self-crosslinks as well. Other resins include those formed by epoxides, which react analogously and also with the cellulose hydroxyl groups, and those formed from aldehydes, which appear to crosslink cellulose reversibly, through hemiacetal bonds, and self-crosslink at amide groups. A discussion of wet-strength resins and their mechanisms is presented in "The Mechanism of Wet-Strength Development in Paper: A Review," by Herbert H. ESPY, Tappi Journal, Vol. 78, No. 4, pages 90-97 (April 1995) as well as in "Chemistry of Paper Wet-Strength. I. A Survey of Mechanisms of Wet-Strength Development," by Lars WESTFELT, Cellulose Chemistry and Technology, Vol. 13, pages 813-825 (1979). The entire contents of both ESPY and WESTFELT are hereby incorporated by reference as though set forth in full herein.
According to ESPY, a wet-strength resin should exhibit four key attributes. These resins should first be water soluble, allowing for an even dispersion and effective distribution over the cellulose fibers. Next, the resins should have some cationic character, inherent or otherwise, facilitating their adsorption onto anionic fibers in the pulp. The resins should also be polymeric, with higher molecular weight polymers apparently forming stronger bonds. Finally, the resins should be reactive, a quality which allows them to be crosslinked to both themselves and to the cellulose in the paper.
Resins comparable to those used for increasing paper strength also find application in creping adhesives. In the manufacture of specific paper products, such as facial tissue, bathroom tissue, or paper towels, the paper web is subjected to a creping process in order to give the paper product desirable characteristics, such as softness and bulk. Typically, the creping process involves adhering the web, a cellulose web in the case of paper, to a rotating creping cylinder, such as that used in a Yankee dryer. The adhered web is then detached with a doctor blade. The impact of the web against the blade disrupts fiber-to-fiber bonds within the web, causing the web to wrinkle, or pucker.
The extent of creping action is dependent on several factors, including the degree of adhesion between the web and the surface of the creping cylinder. Greater adhesion between the web and cylinder results in increased softness, albeit generally with some loss of strength. In order to increase adhesion, a creping adhesive is often used. In addition, creping adhesives can also reduce the wear on a dryer surface, provide lubrication between a doctor blade and a dryer surface, reduce chemical corrosion, and control the extent of creping. Ideally, a creping adhesive adheres the sheet just tightly enough to the drum to produce a good crepe, imparting absorbency and softness to the final product, with a minimal loss of paper strength. However, if adhesion of the web to the dryer drum is too strong, the sheet may pick or even "plug," i.e., underride the doctor blade, and wrap around the dryer drum. On the other hand, if adhesion is too weak, the sheet will lift off too easily and undergo too little creping.
Examples of creping agents are disclosed in U.S. Pat. No. 5,187,219, to FURMAN, U.S. Pat. No. 5,246,544, to HOLLENBERG et al., U.S. Pat. No. 5,338,807, to ESPY et al., and U.S. Pat. No. 5,374,334, to SOMNESE et al. Other examples of creping agents are disclosed in U.S. Pat. Nos. 4,684,439, 4,788,243, 4,501,640, and 4,528,316, each to SOERENS. FURMAN, HOLLENBERG et al., ESPY et al., SOMNESE et al., and SOERENS U.S. Pat. Nos. '439, '243, '640, and '316, are hereby incorporated by reference as though set forth in full herein.
The present invention advances the field of resin compositions for use in paper making. Many of the resin compositions known in the art are toxic to animals, or can be harmful to the environment. The present invention provides an "environmentally friendly" alternative to the known additives and resins. Embodiments of the present invention are essentially chemically benign, using a biocatalytic process to induce crosslinking in a paper product.
The use of a biocatalytic process to induce polymerization of phenols is known in the art. DORDICK et al. describes the production of polymers produced by horseradish peroxidase-catalyzed coupling of phenols in "Polymerization of Phenols Catalyzed by Peroxidase in Nonaqueous Media," Biotechnology and Bioengineering Vol. 30, pgs. 31-36 (1987). POKORA et al. describes the use of such catalytic processes in the production of developer resins in U.S. Pat. No. 4,647,952 ('952), and expanded on those processes in U.S. Pat. No. 4,900,671 ('671), and 5,153,298 ('298). POKORA also describes the use of polyphenol resins in the production of paper in U.S. Pat. No. 5,110,740 ('740). DORDICK et al. and POKORA et al. U.S. Pat. Nos. '952, '671, '298, and '740, are hereby incorporated by reference as though set forth in full herein.
The use of enzymes to catalyze the polymerization of phenols in monolayers is described by AKKARA et al. in U.S. Pat. No. 5,143,828, and in "Synthesis and Characterization of Polyphenols from Peroxidase-Catalyzed Reactions," Enzyme Microb. Technol. vol. 13, page 521 (June 1991), as well as in BRUNO et al., "Enzyme Catalyzed 2-D Polymerization of Phenol Derivatives on a Langmuir-Blodgett Trough," Polymer Reprints, Vol. 32, No. 1, pgs. 232-233 (1991). The enzyme-catalyzed formation of polyesters is described in U.S. Pat. No. 5,147,791, to MORROW et al. AKKARA et al., BRUNO et al., and MORROW et al., are hereby incorporated by reference as though set forth in full herein.
The present invention provides novel and "environmentally friendly" methods and resin and adhesive compositions. Such compositions are particularly useful in the paper making process.